"A genome-wide RNAi screen for neuronal cell fate mutants" The regulatory mechanisms that generate individual neuronal cell types in the nervous system are incompletely understood. Genetic mutant screens in model systems as well as reverse genetic approaches in vertebrates have yielded valuable insights into the mechanisms of neuronal diversification as these approaches have uncovered genes involved in these processes. We propose here to use a genome-wide RNA interference (RNAi)-based reverse genetics approach in the amenable model organism C. elegans to uncover genes involved in controlling the specification of a pair of sensory neurons, called the ASE neurons. The questions that we will address are: (1) what are the genes required for the ASE neurons to be generated and correctly specified;(2) as the two ASE neurons display the intriguing feature of showing left/right asymmetric features in the form of left/right asymmetrically expressed chemoreceptor genes, we wish to identify genes involved in this left/right asymmetric developmental program. So far, we have finished RNAi analysis of the chromosome I (2446 clones) and have identified 14 RNAi clones that lead to a reproducible defect in the development of the ASE neurons. We propose here to scale up this approach to all six chromosomes, leading to an estimated recovery of 6 x 14 = 84 genes potentially involved in ASE neuron development. The framework of an exploratory two-year R03 grant provides us with the opportunity to build such a collection of genes with a role in ASE development. This collection will provide an invaluable resource and starting point for a in-depth and hypothesis-driven gene-by-gene analysis in the future, eventually leading to a detailed understanding of the developmental program that leads to the specification of a single neuron class. PUBLIC HEALTH RELEVANCE: "A genome-wide RNAi screen for neuronal cell fate mutants" This grant proposal sets out to identify genes involved in neuronal development using the nematode C. elegans as a model system. We will use an RNA interference-based screen to identify genes that are required for an individual sensory neuron class to develop and to adopt its left/right asymmetric features in an appropriate manner.